New insights on low-mass dark matter subhalo tidal tracks via numerical simulations

ABSTRACT Several studies assert that dark matter (DM) subhaloes without a baryonic counterpart and with an inner cusp always survive. We conduct numerical simulations to analyse the evolution of the circular velocity peaks ($V_\mathrm{max}$, and its radial value $r_\mathrm{max}$) and concentration of low-mass DM subhaloes under tidal stripping. We employ the improved version of the dash code introduced in the subhalo-survival work of A. Aguirre-Santaella et al. We follow the tidal evolution of a single DM subhalo orbiting a Milky Way (MW)-size halo modelled with a baryonic disc and a bulge representing the MW’s mass distribution, accounting for the time-evolving gravitational potential of the MW. We simulate subhaloes with unprecedented accuracy, varying their initial concentration, orbital parameters, and inner slope. Unlike previous literature, we examine the evolution of subhalo structural parameters – tidal tracks – not only at orbit apocentres but also at pericentres, finding in the former case both similarities and differences –particularly pronounced for prompt cusps. Overall, $r_\mathrm{max}$ shrinks more than $V_\mathrm{max}$, leading to a continuous rise of subhalo concentration with time. The velocity concentration at present is around two orders of magnitude higher than the one at infall – about an order of magnitude more compared to the increase found for field haloes – being comparatively larger for pericentre tidal tracks versus apocentres. These findings highlight the importance of tidal effects in reshaping low-mass DM subhaloes, providing insights for future research via simulations and observations, such as correctly interpreting data from galaxy satellite populations, subhalo searches with gravitational lensing or stellar streams, and indirect DM searches.